I have been there a few times myself. Tunnel is a really neat river lake system and I was turned on to it by a fellow OGF'er several years back. I made a few trips there myself while on our annual trip in that area. We made a few day trips and thus we did not navigate the lake nearly as far as it allows. We put in at the southeast end at what they call the Hooverville landing. The lake goes several miles upstream and widens significantly in the middle then turns back in to a narrow fast flowing river at the upper reaches. I did get to make a fall trip with the fellow OGF'er and we did run pretty much all over the lake. I think specifics of advice from our trip may not be real useful being that it was much later in the year. (October) We did do most of our fishing in the mid-lake and lower lake areas. Walleye bite was non-existent that trip. Hap we not had prior knowledge of the quality of the walleye fishery that it is we would have gone away thinking there were none. We did catch several pike that trip and plenty of smallies. Our earlier day trips produced pretty well for us despite staying within maybe 2 miles of the ramp. Worm harnesses were the ticket that time. Cranks were the ticket on the fall trip.
I will send a message to my buddy. By the way, it is indeed the one you found in your search as I saw your visitor post to him.
Below is a pic of a smallie on the fall trip.